As described in U.S. Pat. No. 4,450,986 to Harasym et al., the discharge port of a vessel for molten metal, which is controlled by a gate valve or the like, often becomes plugged. The unplugging device disclosed in U.S. Pat. No. 4,450,986, the contents of which are incorporated herein, includes a conduit which extends through the wall of an annular member to a lance housing disposed in the annular member, which conduit introduces pressurized gas into the housing. The upper end of the lance housing has a frustrum shaped portion and a reduced diameter cylindrical portion which guides upward movement of the tube. Strict tolerances are required in fabrication of the upper end of the lance housing to ensure that the tube does not become skewed relative to the housing during travel of the tube, so as to prevent binding contact between the tube bottom portion and the interior surface of the housing. The nozzle tip on the tube provides for discharging pressurized gas, while a bottom portion of the tube permits the ingress of a pressurized gas thereto. The reduced diameter portion of the lance housing is elongated so that the relative lengths of the tube and housing are such that the tube does not leave the housing as it travels upwardly to contact plugged material in a vessel discharge port. A pressurized gas for supporting combustion such as oxygen is introduced through the conduit into the lance housing to propel the tube upwardly into contact with the material plugging the discharge port. Heat from the material plugging the discharge port ignites a combustible material positioned within the tube in the presence of the combustion supporting gas. If the pressure of the gas at the tip of the tube is too great, e.g. 250 psi, the discharging gas produces a chilling effect tending to inhibit ignition of the charge of combustible material.
While that device was effective to unplug vessel discharge ports, a further development, as disclosed in my copending application Ser. No. 930,484, the contents of which are incorporated herein, provided for ensuring that the tube is retained in the housing during upward travel and eliminated the chilling effect of the pressurized gas at the upper end of the tube so as to ensure ignition of the charge of combustible material. In that device, a conduit for injection of a gas extends through the wall of an annular member to the lance housing, with the upper and lower ends of the housing disposed, respectively, above and below the conduit elevation. A bushing in the upper end of the housing guides upward movement of a tube which is partially disposed in the housing. The tube carries in its bore a charge of combustible material and the upper end of the tube extends outside the housing while a bottom flared portion of the tube is retained in the housing. The bushing acts to stop the flared portion of the tube from excessive upward movement. A combustible collar mounted on the tube end contains a combustible material, with a portion of the combustible material extending above the elevation of the tube upper end.